Cancer cells are characterized by a strong tendency toward massive proliferation, often at the expense of normal cells. Control mechanisms triggered by membrane-membrane interactions between cells as the cell density increases are bypassed. One of the more promising techniques for studying membrane phenomena is that of spin labeling. A reporter molecule similar in structure to the naturally occurring membrane lipids though containing a paramagnetic nitroxide group is diffused into a membrane system. Important information about the loal environment of the probe within the biological membrane can be secured from an analysis of the electron spin resonance spectra of the nitroxide reporter group. In continuing our work with new nitroxide lipid spin labels (see, inter alia, J.F.W. Keana, S.B. Keana and D. Beetham, J. Am. Chem. Soc., 89, 3055 (1967); 93, 2808 (1971); 97, 1273 (1975); 98, 3052 (1976)), we intend to determine the polar headgroup and fatty acid side chain specificity in the lipid-protein and lipid-lipid interactions in three important transmembranous enzymes: cytochrome oxidase, Na ion - K ion ATPase and Ca ion-dependent ATPase, using techniques and methods of analysis already in use at the University of Oregon (see, inter alia, P.C. Jost, K.K. Nadakavukaren and O.H. Griffith, Biochemistry, in press). Central to this effort is the synthesis of several new well defined spin labeled lipids which are close structural analogs to important lipid components of biological membranes.